CSS parser parses "foo, bar { decls }" into two separate rules -- one
for foo and one for bar. So ParseRule() has to return an array of
rules, not just a rule. r=dbaron, sr=jst
media rules implement nsIDOMCSSMediaRule. Fix insertRule() to be able
to insert into the middle of a rule list. Fix issues with stylesheets
not getting dirtied when media lists are modified. bug 93977,
r=pierre, sr=jst
